Wavelet transform based phase extraction for interferometer signal analysis

Phase or its associated derivative of signal carries very important information, particularly in the application of interferometry technique in non contact measurement, where measurand such as displacement, strain, velocity etc are encoded in the phase of a fringe signal. In most of the dynamic applications this interferometric signal becomes non stationary in nature. Fourier transform is not suitable for extracting the phase of a non stationary signal. Joint time frequency analysis tool such as STFT (Short Time Fourier Transform) may be applied but it has limitation of fixed resolution. On the other hand CWT (Continuous Wavelet Transform) is suitable as it uses adaptive time window which overcomes the fixed resolution problem in STFT. Present work reports the development of two different phase extraction algorithm namely phase estimation and frequency estimation technique based on CWT. Finally these algorithms are validated with simulated signal as well as experimental data and relative merits of these two approaches are discussed and results are presented.